1. Field of the Invention
The present invention relates to a technique for extracting a contour of a cross plane area, which is obtained by causing a desired color plane to cross a gamut that represents a color reproducible range of a device, such as a printer, a monitor, or a scanner, in order to enable the user to recognize the exact shape of the gamut.
2. Description of the Related Art
All the colors reproducible by a certain device are plotted as color points in an adequate color space, for example, in an L*a*b* (L*, a*, and b* are hereinafter simply expressed as L, a, and b) color space of CIE (Commission Internationale de Elclairage). This gives a color solid in the color space. The color solid is a gamut characteristic of the certain device and represents a total range of the colors reproducible by the device. The surface of the gamut corresponds to the limit of the colors reproducible by the device.
The shape of the gamut depends upon the type of the device, such as a printer, amonitor, or a scanner, andmore specifically upon the individual devices.
A proposed method for enabling the user to recognize the shape of the gamut is disclosed in, for example, European Patent Publication No. 0665682.
This proposed method first specifies a plurality of color points arranged at equal intervals along the respective coordinate axes in the Lab color space as representative color points included in a gamut of a certain device. Apredetermined color plane perpendicular to the axis L (that is, a face of identical brightness) is then set to cross the gamut and pass through a plurality of representative color points. A plurality of representative color points that are arranged at equal intervals along the axis a and the axis b accordingly exist in the area of a cross plane of the color plane and the gamut. The method then connects representative color points located in the outer-most portion among the plurality of representative color points existing in the cross plane area, so as to extract an outer line corresponding to a part of the contour of the cross plane area. The position of the color plane to cross the gamut is then shifted along the axis L by the interval between the representative color points, and the same process is repeated to extract an outer line corresponding to another part of the contour of the cross plane area. This method enables the user to finally recognize the exact shape of the gamut.
Another proposed method for enabling the user to recognize the shape of the gamut causes a color plane including the axis L (that is, a face of identical hue) to cross the gamut.
In the related art techniques, a color plane crossing the gamut is set to pass through a plurality of representative color points. These techniques accordingly do not enable the contour of a cross plane area, which is obtained by causing a color plane arranged at an arbitrary position (for example, a color plane arranged to pass between the representative color points) to cross the gamut, to be accurately extracted.
The related art techniques set only either the color planes perpendicular to the axis L (that is, the faces of identical brightness) or the color planes including the axis L (that is, the faces of identical hue) to cross the gamut, in order to extract outer lines corresponding to the contour of a cross plane area with respect to the faces of identical brightness or the faces of identical hue. These techniques are not well applicable to extract the contour of a cross plane area obtained by causing a color plane that is other than the face of identical brightness or the face of identical hue but is arranged in an arbitrary orientation to cross the gamut.